This application claims priority to Korean Application No. 2000-73807, filed Dec. 6, 2000, the disclosure of which is hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to methods of manufacturing semiconductor devices, and more particularly, to methods of forming thin films on substrates.
2. Background of the Invention
A thin film can be used as a dielectric layer of a semiconductor device, a transparent electrical conductor of a liquid crystal display, and a protective layer of an electroluminescent thin film display, for example. In particular, a thin film used as a dielectric layer of a semiconductor device should have limited impurities or defects therein and at the interface of the film in order to ensure high capacitance and limit leakage current. The step coverage and uniformity of a thin film should also be excellent, particularly when used in semiconductor device applications.
However, it is often difficult to obtain excellent step coverage if a thin film is formed using a conventional chemical vapor deposition (CVD) method or physical vapor deposition (PVD) method. Particularly, in a conventional CVD method, a dielectric layer having relatively good step coverage can be obtained by a deposition process using a surface kinetic mode, but reactants, which are used in depositing a dielectric layer, are typically conveyed to a substrate so that it is often difficult to control step coverage.
In order to overcome the above problems, methods have been proposed for forming thin films that can obtain generally good step coverage on the whole by periodically providing reactants to the surface of the substrate on which a thin film will be formed, and activating surface kinetic areas. These methods are, for example, ALD, cyclic CVD, digital CVD, and advanced CVD. However, if a thin film is formed using these methods, unnecessary atoms contained in a chemical ligand forming reactants may remain within the thin film and become impurities, or create particles on the surface of the substrate. By-products produced in a thin film manufacturing process may have significant influence on generating impurities or particles within the thin film.
In these methods, elements that are used in forming a thin film are typically conveyed to a substrate on which a thin film is formed in a high vapor pressure state. Vapor may also be conveyed to the substrate as a reactant, such as a metalorganic precursor or metal halides. To minimize impurities within a thin film, metal elements, organic ligands and/or halides, which are among the reactants typically conveyed to the substrate, may be removed by decomposition in the CVD method. However, in an ALD method, impurities are frequently removed by chemical exchange. That is, in an ALD method, necessary source gases are typically not mixed within a reaction chamber. Instead, each of the gases typically flows by way of pulsing. For example, if a thin film is formed using a first source gas and a second source gas, the first source gas initially flows into the reaction chamber where it is chemisorbed on the substrate, and then the second source gas flows into the reaction chamber where it is then chemisorbed on the substrate.
An Si3N4 thin film can be formed using SiCl4 and NH3 in a CVD or ALD method through the following reaction:
xe2x80x833SiCl4+4NH3xe2x86x92Si3N4+12HCl
Here, in the CVD method, SiCl4 and NH3 are sequentially conveyed to a substrate, which is maintained at a temperature of 550xc2x0 C. or higher, and an Si3N4 thin film is formed by thermal decomposition and HCl is produced as a by-product. On the other hand, in the ALD method, SiCl4 is chemisorbed on the substrate, which is maintained at a relatively low temperature of about 400xc2x0 C. and NH3 is conveyed over the result, so that one layer of an Si3N4 layer is formed by chemical exchange and HCl is produced as a by-product. The HCl by-product may also react with NH3 provided as a reaction gas to form NH4Cl. Accordingly, these deposition processes may require frequent cleaning steps, and may also increase down time in the manufacture of semiconductor devices. By products, such as NH4Cl, may also cause a large quantity of particles to be present during a thin film manufacturing process, and these particles may cause a deterioration in the electric characteristics of the thin film.
According to a first embodiment of the present invention, a first reactant containing a halogen is provided on a semiconductor substrate in order to chemisorb a first reactant adsorption layer combined with hydrogen on the semiconductor substrate. Activated hydrogen gas is provided to the first reactant adsorption layer in order to remove the halogen from the first reactant adsorption layer. A second reactant is provided to the first reactant adsorption layer from which the halogen is removed in order to chemisorb a second reactant adsorption layer and thereby form a solid thin film. The step of providing activated hydrogen gas may include activating by remote-plasma. The solid thin film can be formed as a monoatomic nitride, a compound nitride, a monoatomic oxide, or a compound oxide.
According to a first aspect of the present invention, a method for forming a thin film further comprises a step of removing by-products from the first reactant adsorption layer before providing the activated hydrogen gas. Also, before providing the second reactant and after providing the activated hydrogen gas, a step of removing by-products may be performed. Purging using an inert gas or pumping can be used for removing the by-products. Furthermore, the step of providing the first reactant, the step of providing the activated hydrogen gas, and the step of providing the second reactant can be sequentially repeated several times until a thin film of a desired thickness is obtained.
In a method for forming a thin film according to a second embodiment of the present invention, silicon source gas containing a halogen is provided on the semiconductor substrate in order to chemisorb a silicon adsorption layer combined with a halogen on the semiconductor substrate. Activated hydrogen gas is provided to the silicon adsorption layer in order to remove the halogen from the silicon adsorption layer. Nitrogen source gas is then provided to the silicon adsorption layer (from which the halogen is removed) to form a silicon nitride layer.
According to a second embodiment of the present invention, a method of forming a thin film includes forming a first layer that comprises a first element and is chemisorbed to a surface of a substrate. The first layer is preferably formed by exposing the surface of the substrate to a first source gas having molecules therein that comprise the first element and a halogen. The first layer is then exposed to an activated hydrogen gas so that halogens associated with the first layer become bound to hydrogen provided by the activated hydrogen gas. The first layer is then converted to a thin film that comprises the first element and a second element, by exposing a surface of the first layer to a second source gas having molecules therein that comprise the second element. The step of exposing the first layer to an activated hydrogen gas may be performed simultaneously with a step of generating the activated hydrogen gas using a plasma generated remote from the substrate. This step may also be preceded by a step of exposing the first layer to an inert gas and may be followed by a step of exposing the first layer to an inert gas.